Substrate processing tool with integrated metrology and method of using

ABSTRACT

A substrate processing tool configured for performing integrated substrate processing and substrate metrology, and methods of processing a substrate. The substrate processing tool includes a substrate transfer chamber, a plurality of substrate processing chambers coupled to the substrate transfer chamber, and a substrate metrology module coupled to the substrate transfer chamber. A substrate processing method includes processing a substrate in a first substrate processing chamber of a substrate processing tool, transferring the substrate from the first substrate processing chamber through a substrate transfer chamber to a substrate metrology module in the substrate processing tool, performing metrology on the substrate in the substrate metrology module, transferring the substrate from the substrate metrology module to a second substrate processing chamber through the substrate transfer chamber, and processing the substrate in the second substrate processing chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims priority to U.S. ProvisionalPatent Application Ser. No. 62/645,685 filed on Mar. 20, 2018, theentire contents of which are herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to substrate processing, and moreparticularly, to a substrate processing tool configured for performingintegrated substrate processing and substrate metrology, and a method ofusing.

BACKGROUND OF THE INVENTION

As smaller transistors are manufactured, the critical dimension (CD) orresolution of patterned features is becoming more challenging toproduce. Self-aligned patterning needs to replace overlay-drivenpatterning so that cost-effective scaling can continue even after EUVintroduction. Patterning options that enable reduced variability, extendscaling and enhanced CD and process control are needed, however, it'sgetting extremely difficult to produce scaled devices at reasonably lowcost. Selective deposition can significantly reduce the cost associatedwith advanced patterning. Selective deposition of thin films such as gapfill, area selective deposition of dielectrics and metals on specificsubstrates, and selective hard masks are key steps in patterning inhighly scaled technology nodes.

SUMMARY OF THE INVENTION

Embodiments of the invention describe a substrate processing toolconfigured for performing integrated substrate processing and substratemetrology, and methods of processing a substrate.

According to one embodiment, a substrate processing tool includes asubstrate transfer chamber, a plurality of substrate processing chamberscoupled to the substrate transfer chamber, and a substrate metrologymodule coupled to the substrate transfer chamber.

According to one embodiment, a substrate processing method includesprocessing a substrate in a first substrate processing chamber of asubstrate processing tool, transferring the substrate from the firstsubstrate processing chamber through a substrate transfer chamber to asubstrate metrology module in the substrate processing tool, performingmetrology on the substrate in the substrate metrology module,transferring the substrate from the substrate metrology module to asecond substrate processing chamber through the substrate transferchamber, and processing the substrate in the second substrate processingchamber.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of embodiments of the invention and many ofthe attendant advantages thereof will become readily apparent withreference to the following detailed description, particularly whenconsidered in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a substrate processing tool configuredfor performing integrated substrate processing and substrate metrologyaccording to an embodiment of the invention;

FIGS. 2A-2E show through schematic cross-sectional views a method ofarea selective film formation according to an embodiment of theinvention;

FIG. 3 is a process flow diagram for performing integrated substrateprocessing and substrate metrology according to an embodiment of theinvention; and

FIG. 4 is a process flow diagram for performing integrated substrateprocessing and substrate metrology according to another embodiment ofthe invention.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

Embodiments of the invention describe a substrate processing toolconfigured for performing integrated substrate processing and substratemetrology, and methods of processing a substrate.

Embodiments of the invention address integrated substrate processing andthe need for performing substrate metrology during the integratedsubstrate processing. In one example, during area selective filmdeposition in a substrate processing tool, substrate metrology may beperformed in the processing tool following a film deposition step tomeasure and characterize loss of deposition selectivity and, based onsubstrate metrology data, perform removal of undesired film nuclei toachieve selective film formation. The results from the substratemetrology step may be used to tune the film nuclei removal step based onvariation in the film deposition step. Further, artificial intelligence(AI) may be used to analyze the substrate metrology results and predictfuture film thickness and film deposition selectivity.

FIG. 1 is a schematic diagram of a substrate processing tool configuredfor performing integrated substrate processing and substrate metrologyaccording to embodiments of the invention. The substrate processing tool100 contains a substrate (wafer) transfer system 101 that includescassette modules 101A, 101B, and 101C, and a substrate alignment module101D. Load-lock chambers 102A and 102B, and substrate metrology module102C, are coupled to the substrate transfer system 101. The substratetransfer system 101 is maintained at atmospheric pressure but a cleanenvironment is provided by purging with an inert gas. The load lockchambers 102A and 102B are coupled to a substrate transfer chamber 103and may be used for transferring substrates from the substrate transfersystem 101 to the substrate transfer chamber 103. The substrate transferchamber 103 may be maintained at a very low base pressure (e.g., 5×10⁻⁸Torr, or lower) or constantly purged with an inert gas.

The substrate metrology module 102C may be operated under atmosphericpressure or operated under vacuum conditions and can include one or moreanalytical tools that are capable of measuring one or more material andelectronic properties of a substrate and/or thin films and layersdeposited on a substrate. Some or all components of the one or moreanalytical tools may located in the vacuum environment in the substratemetrology module 102C. In one example, a light source may be positionedoutside the substrate metrology module 102C and light from the lightsource may be transmitted into the substrate metrology module 102C andonto a substrate through a window. Alternatively, the light source maybe positioned inside the substrate metrology module 102C.

Exemplary analytical tools can include X-ray photoelectron spectroscopy(XPS) for measuring elemental composition, empirical formula, chemicalstate and electronic state of materials; X-ray reflectometry (XRR) forcharacterizing surfaces, thin films and multilayers; X-ray fluorescence(XRF) for elemental analysis and chemical analysis of materials;Fourier-transform infrared spectroscopy (FTIR) for characterizingmaterials; ultraviolet/visible (UV/Vis) spectroscopy for measuringthickness and optical properties of thin films; optical scatterometryfor characterizing surfaces, thin films and multilayers; ellipsometryfor characterizing composition, roughness, thickness (depth),crystalline nature, doping concentration, electrical conductivity andother material properties of thin films; and analytical tools formeasuring substrate bow and warp.

Coupled to the substrate transfer chamber 103 are substrate processingchambers 106A-106D that are configured for processing substrates, suchas Si wafers. The Si wafers can, for example, have a diameter of 150 mm,200 mm, 300 mm, 450 mm, or larger than 450 mm. According to oneembodiment of the invention, the first substrate processing chamber 106Acan perform a treatment process on a substrate, and the second substrateprocessing chamber 106B can form a self-aligned monolayer (SAM) on asubstrate. The third substrate processing chamber 106C can etch or cleana substrate, and the fourth substrate processing chamber 106D candeposit a film on a substrate by vapor deposition such as atomic layerdeposition (ALD), plasma-enhanced ALD (PEALD), chemical vapor deposition(CVD), or plasma-enhanced CVD (PECVD). The substrate transfer chamber103 is configured for transferring substrates between any of thesubstrate processing chambers 106A-106D, and into the substratemetrology module 102C. FIG. 1 further shows gate valves G1-G9 thatprovide isolation between adjacent processing tool components. Asdepicted in the embodiment of FIG. 1, the substrate processing chambers106A-106D and the substrate metrology module 102C may be directlycoupled to the substrate transfer chamber 103 by the gate valves G5, G7,G8, G9, and G10. This direct coupling can greatly improve substratethroughput.

The substrate processing tool 100 includes a controller 110 that can becoupled to and control any or all of the tool components depicted inFIG. 1 during the integrated substrate processing and substratemetrology. Alternatively, or in addition, the controller 110 can becoupled to one or more additional controllers/computers (not shown), andthe controller 110 can obtain setup and/or configuration informationfrom an additional controller/computer. The controller 110 can be usedto configure any or all of the substrate processing chambers andprocessing elements, and the controller 110 can collect, provide,process, store, and display data from any or all of the tool components.The controller 110 can comprise a number of applications for controllingany or all of the tool components. For example, controller 110 caninclude a graphic user interface (GUI) component that can provide easyto use interfaces that enable a user to monitor and/or control one ormore tool components.

The controller 110 can include a microprocessor, memory, and a digitalI/O port capable of generating control voltages sufficient tocommunicate, activate inputs, and exchange information with thesubstrate processing tool 100 as well as monitor outputs from thesubstrate processing tool 100. For example, a program stored in thememory may be utilized to activate the inputs of the substrateprocessing tool 100 according to a process recipe in order to performintegrated substrate processing. The controller 110 may be implementedas a general purpose computer system that performs a portion or all ofthe microprocessor based processing steps of the invention in responseto a processor executing one or more sequences of one or moreinstructions contained in a memory. Such instructions may be read intothe controller memory from another computer readable medium, such as ahard disk or a removable media drive. One or more processors in amulti-processing arrangement may also be employed as the controllermicroprocessor to execute the sequences of instructions contained inmain memory. In alternative embodiments, hard-wired circuitry may beused in place of or in combination with software instructions. Thus,embodiments are not limited to any specific combination of hardwarecircuitry and software.

The controller 110 may be locally located relative to the substrateprocessing tool 100, or it may be remotely located relative to thesubstrate processing tool 100. For example, the controller 110 mayexchange data with the substrate processing tool 100 using at least oneof a direct connection, an intranet, the Internet and a wirelessconnection. The controller 110 may be coupled to an intranet at, forexample, a customer site (i.e., a device maker, etc.), or it may becoupled to an intranet at, for example, a vendor site (i.e., anequipment manufacturer). Additionally, for example, the controller 110may be coupled to the Internet. Furthermore, another computer (i.e.,controller, server, etc.) may access, for example, the controller 110 toexchange data via at least one of a direct connection, an intranet, andthe Internet. As also would be appreciated by those skilled in the art,the controller 110 may exchange data with the substrate processing tool100 via a wireless connection.

SUBSTRATE PROCESSING EXAMPLES

Referring now to FIG. 1, FIGS. 2A-2E, and FIG. 3, according to oneembodiment, the substrate processing tool 100 may be configured toperform and monitor a method of area selective deposition on asubstrate. In this embodiment, the substrate 200 contains a base layer202, an exposed surface of a first material layer 204 and an exposedsurface of a second material layer 206. In one example, the substrate200 includes a dielectric layer 204 and a metal layer 206. For example,the metal layer 206 can contain Cu, Al, Ta, Ti, W, Ru, Co, Ni, or Mo.The dielectric layer 204 can, for example, contain SiO₂, a low-kdielectric material, or a high-k dielectric material. Low-k dielectricmaterials have a nominal dielectric constant less than the dielectricconstant of SiO₂, which is approximately 4 (e.g., the dielectricconstant for thermally grown silicon dioxide can range from 3.8 to 3.9).High-k materials have a nominal dielectric constant greater than thedielectric constant of SiO₂.

Low-k dielectric materials may have a dielectric constant of less than3.7, or a dielectric constant ranging from 1.6 to 3.7. Low-k dielectricmaterials can include fluorinated silicon glass (FSG), carbon dopedoxide, a polymer, a SiCOH-containing low-k material, a non-porous low-kmaterial, a porous low-k material, a spin-on dielectric (SOD) low-kmaterial, or any other suitable dielectric material. The low-kdielectric material can include BLACK DIAMOND® (BD) or BLACK DIAMOND® II(BDII) SiCOH material, commercially available from Applied Materials,Inc., or Coral® CVD films commercially available from Novellus Systems,Inc. Other commercially available carbon-containing materials includeSILK® (e.g., SiLK-I, SiLK-J, SiLK-H, SiLK-D, and porous SiLKsemiconductor dielectric resins) and CYCLOTENE® (benzocyclobutene)available from Dow Chemical, and GX-3™, and GX-3P™ semiconductordielectric resins available from Honeywell.

Low-k dielectric materials include porous inorganic-organic hybrid filmscomprised of a single-phase, such as a silicon oxide-based matrix havingCH₃ bonds that hinder full densification of the film during a curing ordeposition process to create small voids (or pores). Stillalternatively, these dielectric layers may include porousinorganic-organic hybrid films comprised of at least two phases, such asa carbon-doped silicon oxide-based matrix having pores of organicmaterial (e.g., porogen) that is decomposed and evaporated during acuring process.

In addition, low-k materials include a silicate-based material, such ashydrogen silsesquioxane (HSQ) or methyl silsesquioxane (MSQ), depositedusing SOD techniques. Examples of such films include FOx® HSQcommercially available from Dow Corning, XLK porous HSQ commerciallyavailable from Dow Corning, and JSR LKD-5109 commercially available fromJSR Microelectronics.

The method further includes, in step 302 of the process flow 300,providing the substrate 200 into the substrate transfer system 101, andthereafter, transferring the substrate 200 into the substrate transferchamber 103.

Thereafter, in step 304, the substrate 200 is optionally transferredinto the substrate metrology module 102C where the substrate 200 ismeasured and characterized.

In step 306, the substrate 200 is optionally transferred into the firstsubstrate processing chamber 106A for treating with a treatment gas. Forexample, the treatment gas can include an oxidizing gas or a reducinggas. In some examples, the oxidizing gas can include O₂, H₂O, H₂O₂,isopropyl alcohol, or a combination thereof, and the reducing gas caninclude H₂ gas. The oxidizing gas may be used to oxidize a surface ofthe first material layer 204 or the second material 206 to improvesubsequent area selective deposition. In one example, the treatment gascan contain or consist of plasma-excited Ar gas.

In step 308, the substrate 200 is optionally transferred into thesubstrate metrology module 102C where the treating of the substrate 200in step 306 is measured and characterized.

Thereafter, the substrate is transferred into the second substrateprocessing chamber 106B where a self-aligned monolayer (SAM) is formedon the substrate 200 in step 310. The SAM may be formed on the substrate200 by exposure to a reactant gas that contains a molecule that iscapable of forming a SAM on the substrate 200. The SAM is a molecularassembly that is formed spontaneously on substrate surfaces byadsorption and organized into more or less large ordered domains. TheSAM can include a molecule that possesses a head group, a tail group,and a functional end group, and the SAM is created by the chemisorptionof head groups onto the substrate 200 from the vapor phase at roomtemperature or above room temperature, followed by a slow organizationof the tail groups. Initially, at small molecular density on thesurface, adsorbate molecules form either a disordered mass of moleculesor form an ordered two-dimensional “lying down phase”, and at highermolecular coverage, over a period of minutes to hours, begin to formthree-dimensional crystalline or semicrystalline structures on thesubstrate surface. The head groups assemble together on the substrate,while the tail groups assemble far from the substrate.

According to one embodiment, the head group of the molecule forming theSAM can include a thiol, a silane, or a phosphonate. Examples of silanesinclude molecule that include C, H, Cl, F, and Si atoms, or C, H, Cl,and Si atoms. Non-limiting examples of the molecule includeperfluorodecyltrichlorosilane (CF₃(CF₂)₇CH₂CH₂SiCl₃),perfluorodecanethiol (CF₃(CF₂)₇CH₂CH₂SH), chlorodecyldimethylsilane(CH₃(CH₂)₈CH₂Si(CH₃)₂Cl), and tertbutyl(chloro)dimethylsilane((CH₃)₃CSi(CH₃)₂Cl)).

The presence of the SAM on a substrate 200 to may be used to enablesubsequent selective film deposition on the first material layer 204(e.g., a dielectric layer) relative to the second material layer 206(e.g., a metal layer). This selective deposition behavior is unexpectedand provides a new method for selectively depositing a film on the firstmaterial layer 204 while preventing or reducing metal oxide depositionon the second material layer 206. It is speculated that the SAM densityis greater on the second material layer 206 relative to on the firstmaterial layer 204, possibly due to higher initial ordering of themolecules on the second material layer 206 relative to on the firstmaterial layer 204. This greater SAM density on the second materiallayer 206 is schematically shown as SAM 208 in FIG. 2B.

Following the formation of the SAM 208 on the substrate 200, in step312, the substrate 200 is optionally transferred into the substratemetrology module 102C where the formation of the SAM 208 on thesubstrate 200 is measured and characterized.

Thereafter, the substrate 200 is transferred into the fourth substrateprocessing chamber 106D where, in step 314, a film 210 (e.g., a metaloxide film) is selectively deposited on the first material layer 204relative to on the second material layer 206 containing the SAM 208 byexposing the substrate 200 to one or more deposition gases. In oneexample, the film 210 may include a metal oxide film that contains HfO₂,ZrO₂, or Al₂O₃. The film 210 may, for example, be deposited by CVD,plasma-enhanced CVD PEALD), ALD or plasma-enhanced ALD (PEALD). In someexamples, the film 210 may be deposited by ALD using alternatingexposures of a metal-containing precursor and an oxidizer (e.g., H₂O,H₂O₂, plasma-excited O₂, or O₃).

As depicted in FIG. 2C, the exposure to the one or more deposition gasesin the third substrate processing chamber 106C may, in addition todepositing the film 210 on the first material layer 204, deposit filmnuclei 210′ on the SAM 208. This loss of deposition selectivity canoccur if the deposition process is carried out for too long or if thedeposition selectivity between the first material layer 204 and the SAM208 is poor. Poor deposition selectivity can also occur if surfacecoverage of the SAM 208 is incomplete and contains voids on the secondmaterial layer 206.

Following the deposition of the film 210 on the substrate 200, in step316, the substrate 200 is transferred into the substrate metrologymodule 102C where the deposition of the film 210 is measured andcharacterized. The characterization can determine the degree ofdeposition selectivity and the removal needed of the film nuclei 210′from the SAM 208.

The film nuclei 210′ on the SAM 208 may be removed using an etchingprocess in order to selectively form the film 210 on the first materiallayer 204. The substrate 200 is transferred into the third substrateprocessing chamber 106C to perform the etching process in step 318.Although the film 210 may also be partially removed by the etchingprocess, the metal oxide nuclei 210′ are expected to etch faster thanthe film 210. The etching process can include a dry etching process, awet etching process, or a combination thereof. In one example, theetching process may include an atomic layer etching (ALE) process. Theresulting substrate 200 shown in FIG. 2D has the film 210 selectivelyformed on the first material layer 204.

Following the etching process, in step 320, the substrate 200 isoptionally transferred into the substrate metrology module 102C wherethe substrate 200 is measured and characterized. The characterizationcan determine the extent of the etching process.

Thereafter, in step 322, the SAM 208 may be removed from the substrate200, for example by etching or cleaning in the third substrateprocessing chamber 106C or by a heat-treatment in the first substrateprocessing chamber 106A.

As schematically shown by process arrow 324, the above-describedsubstrate processing steps 304-322, may be repeated one or more times toincrease the thickness of the film 210 on the substrate 200. Removal andsubsequent repeated deposition of the SAM 208 on the substrate 200 maybe desired if the SAM 208 becomes damaged during the film depositionand/or the etching process and therefore affects the film depositionselectivity.

FIG. 4 is a process flow diagram for performing integrated substrateprocessing and substrate metrology according to an embodiment of theinvention. Also referring to FIG. 1 and FIGS. 2A-2E, the process flowdiagram 400 in FIG. 4 is similar to the process flow diagram 300 in FIG.3 and includes, in step 402, providing a substrate 200 in a substrateprocessing tool 100, where the substrate 200 contains an exposed surfaceof a first material layer 204 and an exposed surface of a secondmaterial layer 206. In one example, the first material layer 204includes a dielectric layer and the second material layer 206 includes ametal layer. The method further includes, in step 404, optionallyperforming substrate metrology, in step 406, optionally treating thesubstrate 200 with a treatment gas, and in step 408, optionallyperforming substrate metrology.

The method further includes, in step 410, forming a SAM 208 on thesubstrate 200, and in step 412, optionally performing substratemetrology. The method further includes, in step 414, depositing a film210 on the first material layer 204 and film nuclei 210′ on the SAM 208,and in step 416, performing substrate metrology. The method furtherincludes, in step 418, removing film nuclei 210′ from the SAM 208, andin step 420, optionally performing substrate metrology. The furtherincludes, in 422, optionally treating the substrate 200 with a treatmentgas. As schematically shown by process arrow 424, the above-describedsubstrate processing steps 412-422, may be repeated one or more times toincrease the thickness of the film 210 on the substrate 200.

A substrate processing tool configured for performing integratedsubstrate processing and substrate metrology, and a method of areaselective deposition have been disclosed in various embodiments. Theforegoing description of the embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formsdisclosed. This description and the claims following include terms thatare used for descriptive purposes only and are not to be construed aslimiting. Persons skilled in the relevant art can appreciate that manymodifications and variations are possible in light of the aboveteaching. Persons skilled in the art will recognize various equivalentcombinations and substitutions for various components shown in theFigures. It is therefore intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto.

What is claimed is:
 1. A substrate processing tool, comprising: asubstrate transfer chamber; a plurality of substrate processing chamberscoupled to the substrate transfer chamber; and a substrate metrologymodule coupled to the substrate transfer chamber.
 2. The substrateprocessing tool of claim 1, wherein the substrate metrology moduleincludes one or more analytical tools that measure one or more materialproperties of a substrate or thin films and layers formed on asubstrate.
 3. The substrate processing tool of claim 1, wherein thesubstrate transfer chamber includes a substrate transfer robot.
 4. Thesubstrate processing tool of claim 1, wherein the plurality of substrateprocessing chambers include: a first substrate processing chamberconfigured for performing a self-assembled monolayer (SAM) process; asecond substrate processing chamber configured for performing a filmdeposition process; and a third substrate processing chamber configuredfor performing an etching process.
 5. The substrate processing tool ofclaim 4, wherein the second substrate processing chamber is configuredfor performing a film deposition process by atomic layer deposition(ALD), plasma-enhanced ALD (PEALD), chemical vapor deposition (CVD), orplasma-enhanced CVD (PECVD).
 6. The substrate processing tool of claim4, further comprising a fourth substrate processing chamber configuredfor performing a treatment process using a reactive treatment gas,heat-treatment, or a combination thereof.
 7. The substrate processingtool of claim 1, wherein the substrate metrology module is directlycoupled to the substrate transfer chamber by a gate valve.
 8. Asubstrate processing method, comprising: processing a substrate in afirst substrate processing chamber of a substrate processing tool;transferring the substrate from the first substrate processing chamberthrough a substrate transfer chamber to a substrate metrology module inthe substrate processing tool; performing metrology on the substrate inthe substrate metrology module; transferring the substrate from thesubstrate metrology module to a second substrate processing chamberthrough the substrate transfer chamber; and processing the substrate inthe second substrate processing chamber.
 9. The substrate processingmethod of claim 8, wherein the substrate metrology module is directlycoupled to the substrate transfer chamber by a gate valve.
 10. Thesubstrate processing method of claim 8, wherein the first substrateprocessing chamber is configured for performing a film depositionprocess, and the second processing chamber is configured for performingan etching process.
 11. The substrate processing method of claim 8,wherein the substrate metrology module includes one or more analyticaltools that measure one or more material properties of a substrate orthin films and layers formed on the substrate.
 12. A substrateprocessing method, comprising providing a substrate in a substrateprocessing tool, the substrate containing an exposed surface of a firstmaterial layer and an exposed surface of a second material layer;forming a self-assembled monolayer (SAM) on the substrate in a firstsubstrate processing chamber; transferring the substrate from the firstsubstrate processing chamber through a substrate transfer chamber to asecond substrate processing chamber; and depositing a film on the firstmaterial layer and film nuclei on the self-assembled monolayer in thesecond substrate processing chamber; transferring the substrate from thesecond substrate processing chamber through the substrate transferchamber to a substrate metrology module; performing metrology on thefilm in the substrate metrology module; transferring the substrate fromthe substrate metrology module through the substrate transfer chamber toa third substrate processing chamber; and removing the film nuclei fromthe self-assembled monolayer by etching in the third substrateprocessing chamber.
 13. The substrate processing method of claim 12,wherein the substrate metrology module is directly coupled to thesubstrate transfer chamber by a gate valve.
 14. The substrate processingmethod of claim 12, further comprising performing a treatment process onthe substrate in a fourth substrate processing chamber using a reactivetreatment gas, heat-treatment, or a combination thereof.
 15. Thesubstrate processing method of claim 12, wherein the first materiallayer includes a dielectric layer.
 16. The substrate processing methodof claim 12, wherein the second material layer includes a metal layer.17. The substrate processing method of claim 16, wherein the metal layercontains Cu, Al, Ta, Ti, W, Ru, Co, Ni, or Mo.
 18. The substrateprocessing method of claim 12, wherein the film includes a metal oxide.19. The substrate processing method of claim 12, wherein a density ofthe SAM is greater on the second material layer than on the firstmaterial layer.
 20. The substrate processing method of claim 12, whereinthe SAM includes a plurality of molecules containing a head group, atail group, and a functional end group, wherein the head group includesa thiol, a silane, or a phosphonate.